Epoxy resins and silane aqueous co-dispersions and the uses thereof

Description

[0001] This invention relates to a process to prepare an aqueous co-dispersion of epoxy resins with a silane as part A of a curable composition and in which the part B comprises a hardener.

[0002] Epoxy resins are used already for a long time and different vehicles (solvent, powder) have been tried. Due to environmental concern the development of aqueous systems has been more and more proposed to the industry for several types of end applications. It is known that adding silane into water based dispersion leads to unstable end product.

[0003] The US 6,221,934 describes stable aqueous emulsions of epoxy resins by using an epoxy-functional surfactant prepared by reacting an amidoamine with the epoxy groups. The epoxy resin is further cured with an amine water compatible oligomer.

[0004] In the field of protective coating several options have been proposed, one of them is the use of a metal such as zinc (WO 2011/112452) in combination with water based epoxy resins to provide a stable formulation with good protective properties. The protection of metal surface is also improved by the use of silane derivatives and specially epoxy functional silanes. These derivatives are well known to improve the adhesion of the coating to the metal. The trend is now to provide water based systems to the coating industry, however the silane derivatives formulated in an epoxy water dispersed system show often poor storage stability.

[0005] The invention describes stable silane containing waterborne epoxy primer formulations. The way to stabilize the silanes in presence of water is described, as well as the way to formulate the waterborne epoxy primers.

[0006] Silane adhesion promoters are often used in epoxy primers, especially when adhesion to smooth steel is required. However, the water-based silane containing pigment pastes usually show reduced storage stability of a few weeks or a few months. After a few days or maximum 3 months paste storage, the adhesion is usually reduced or completely gone.

[0007] Emulsions of some silanes are described in the literature but not in presence of epoxy resin or other pigments or coating additives (EP 1896522).

[0008] The present invention is about stable waterborne epoxy primers containing silane adhesion promoter with at least 3 months storage stability and even above 1 year storage stability. We have found that after this storage the adhesion to smooth steel is maintained to the initial value. The process conditions to be used in order to achieve this stability are part of this invention.

[0009] Objects of this invention are as follows:

(1) a process to make an aqueous co-dispersion of epoxy resins and at least a silane or silane oligomers,

(2)a composition comprising epoxy resin emulsion or dispersion and the silane emulsion

(3)the above epoxy composition formulated in the presence of a curing agent, as paint composition.

[0010] The composition of the invention may also contain solvents, pigments, fillers and additives known from the skilled person in the art.

[0011] The epoxy resins useful for the invention are based on: bisphenol type epoxy resin obtained by condensation between bisphenol A [2,2-bis(4'hydroxyphenyl)-propane] or bisphenol F and epichlorohydrin or the like. Commercially available bisphenol type epoxy resins are liquid or solid and have a molecular weight of about 350 to about 3750 and an epoxy equivalent of about 180 to about 3500. Preferred examples of the aqueous epoxy resins are bisphenol-A and/or bisphenol-F based epoxy resins having from 350 to 3750 molecular weight, nonionically dispersed in water with or without glycol ether cosolvents. Commercial examples of the aqueous epoxy resins include, for example, Bisphenol A resins, like EPI-REZ Resin 3510-W-60 (emulsion), EPI-REZ Resin 3520-WY-55, EPI-REZ Resin 3521-WY-53, EPI-REZ Resin 3523-WH-53, EPI-REZ Resin 6520-WH-53, EPI-REZ Resin 3540-WY-55, EPI-REZ Resin 3546-WH-53 EPI-REZ Resin 5522-WY-55, EPI-REZ Resin 6530-WH-53 (dispersions),all available from Momentive Specialty Chemical Inc.

[0012] The curing agents of the invention are compatible with aqueous dispersions without adding acid salts. Commercial examples of the aqueous curing agents are EPIKURE Curing Agent 6870-W-53 or EPIKURE Curing Agent 8545-W-52 and the like available from Momentive Specialty Chemical Inc.

[0013] These curable systems contain one or more epoxy resins and one or more curing agents.

[0014] These aqueous curable epoxy resin systems can be further catalyzed with a commercially available tertiary amine accelerator, such as 2,4,6-tris(dimethyl aminomethyl phenol) or phenols to cure at lower temperatures. Examples of such materials are EPIKURE Curing Agent 3253 from Momentive Specialty Chemical Inc or DMP-30 from Rohm and Haas.

[0015] As the surface active agent, there can be mentioned, for example, derivatives of polyethylene and / or polypropylene gycol, such as or Pluronics or Synperonics , surfactants based on natural fatty acids(as stearic acid) and sorbitol such as Span 60, ethoxylated sorbitan ester based on palmetic acid such as Tween 40.

[0016] These aqueous epoxy resin systems can serve as components of paints and coatings for application to substrates such as, for example, metal, wood, glass substrates and cementitious structures. To prepare such paints and coatings, these resins or amines are blended with primary, extender and anti-corrosive pigments, and optionally, additives such as surfactants, antifoam agents, rheology modifiers and mar and slip reagents. The selection and amount of these pigments and additives depends on the intended application of the paint and is generally recognized by those skilled in the art.

[0017] The process conditions to apply in order to achieve a storage stable aqueous epoxy resin formulation containing a silane are as follow:

the silane is emulsified in presence of emulsifier such as the one given above at temperature between 20 and 65°C, this silane emulsion is further blended at room temperature with an epoxy water based dispersion; an alternative process is as follow: the liquid silane is added at the end of the process to prepare the water-based epoxy resin dispersion and before the final dilution to the required solids content; to further improve the stability the silane can be blended with a liquid mono-epoxy aliphatic compound such as Cardura CE-10.

[0018] In another embodiment the epoxy containing the silane dispersion or emulsion can further be mixed with pigments or additives into a fully formulation paint part A.

Examples

[0019] Epoxy-silane water based dispersion

Example of cold-blending: MP200 emulsion preparation

[0020] In the case of cold blending, the silane emulsion can be produced by various methods and with a large range of surfactants.

Recipe: Silane oligomer:	CoatOsil MP200	40%
	Span 60	2%
	Tween 40	2%
	Water	56%

1) Emulsion by inversion method

[0021] In a beaker glass, 2g Span 60 and 2g Tween 40 are weighed and heated in a 60°C water bath to melt the solid surfactant. CoatOsil MP200 (40g) are added and the mixture are stirred with a mechanical stirrer for several minutes until homogenous. Cool the mixture to below 35°C and increase the stir speed to 3500 rpm. Gradually add water until the mixture inverts around 66% solids. Continue mixing for a few minutes and check particle size. When the desired particle size is reached, add the remainder of the water to dilute the emulsion to the required solids content.

2) Emulsion by solid addition method

[0022] In a beaker glass, 21g of water is heated in a 60°C water bath. The surfactants Span 60 (2g) and Tween 40 (2g) are added and stirred with a mechanical stirrer to melt the solid surfactant. Once homogenous, the mixture is cooled down to below 35°C. The stir speed is increased to 3500 rpm and the CoatOsil MP200 is added gradually. After addition, continue stirring until the desired particle size is reached. Dilute the emulsion to the required solid content by adding the remainder of the water.

3) Variations on the recipe

[0023] The surfactants Span and Tween can be replaced by a mixture of poloxamers (block copolymer based on polyethylene and polypropylene oxide) like Pluronic® from BASF.

[0024] The above described emulsification methods can be applied.

[0025] The silane emulsion is blended with one epoxy resin dispersion or a blend of epoxy dispersions. Example is with EPI-REZ Resin 6530-WH-53.

[0026] The "in situ" preparation method:

a liquid epoxy resin (Epikote 828 533 g) is fused with bisphenol A (122 g) until the desired molecular weight is reached. This epoxy resin is further advanced with a blend of polyethylene and

propylene glycols in the presence of a catalyst 1.25 g (Anchor 1040). The resulting epoxy is dissolved in an appropriate solvent and water is added until the resin is dispersed into the water continuous phase, at this stage 53 g of a 50/50 weight blend of CoatOsil MP200 and Cardura CE-10 is added to the epoxy dispersion after stirring, more water is added to dilute the dispersion to the desired solids content.

[0027] Fusion conditions: The liquid epoxy resin and bis phenol A in the presence of triphenylphosphonium (TPP) are heated to 165°C. After 45 min a sample is taken to confirm the required epoxy group content (EGC). The resin is cooled down by addition of E4000 and P900 to 150°C.The catalyst Anchor 1040 is added and the EGC is reached after 1 hour of reaction at 150°C.

[0028] Preparation of the paint composition, the paint consists out of a Part A and a Part B. The Part A is always the part of the paint containing the pigments and fillers currently used in anticorrosive paints, this could be based on the epoxy resin or on the curing agent; the silane can be in the Part A or in the Part B. If the silane oligomer is used with the Part A it is often added in the so called "let down" of the process.

Paint example 1 (comparative)

[0029] The (pure) CoatOSil MP200 silane oligomer (further named MP200) and the CoatOSil MP200 emulsion were used as additives in the let down of the primers (Part A). This was compared with no silane in the paint. Also, stability of the paste was checked after 4 months.

[0030] Here are the 2 reference starting formulations without any silane. 5g pure MP200 were added for 1000g formulation. For the MP200 emulsion, this corresponds to 12.71g MP200 emulsion.

Table 1a: comparative composition Example 1a

Ingredients Part A	Weight, g
EPI-REZ 3520-WY-55	300
Dowanol PPH (Dow)	28.05
EFKA2526 (EFKA)	2.74
Ti-Pure R960 (DuPont)	91.19
Tremin 283-600EST (Sibelco)	89.55
Albawhite 80 (Sachtleben)	61.06
Heucophos CAPP (Heubach)	84.93
MicaS (Aspanger)	6.54
EPI-REZ 3520-WY-55	149.43
Silane	See note above
Demi-water	92.41

Ingredients Part B
EPIKURE 8545-W-52	93.19
Raybo 80 (Raybo Chemicals)	0.9
Total	1000

Table 1b: comparative composition Example 1b

Ingredients Part A	Weight, g
EPI-REZ 6520-WH-53	300
Dowanol PPH (Dow)	27.23
EFKA2526 (EFKA)	2.66
Ti-Pure R960 (DuPont)	88.53
Tremin 283-600EST (Sibelco)	86.93
Albawhite 80 (Sachtleben)	59.27
Heucophos CAPP (Heubach)	82.45
MicaS (Aspanger)	6.35
EPI-REZ 6520-WH-53	142.16
Silane	See note above
Demi-water	89.71

Ingredients Part B
EPIKURE 6870-W-53	113.84
Raybo 80 (Raybo Chemicals)	0.88
Total	1000

[0031] Panels were sprayed with these formulations. The cure schedule was 20 minutes at 70°C then 2 weeks at 23°C. The panels were exposed for 500 hours in neutral salt spray, and then evaluated for corrosion and adhesion, according to ISO 7253-84 (saltspray resistance).

[0032] The silane is needed to get good performance on smooth steel panels (Gardobond OC). However a very significant decrease in performance was observed on smooth steel after 4 months storage of the Part A containing the silane oligomer. This shows that the silane is no more efficient as an adhesion promoter after 4 months storage; see Table 2. Adhesion was tested according to a visual evalution at the cross (knife scratching) after exposure 500 hours saltspray exposure (rating 5 = perfect, 1 = poor)

Table 2: stability of the silane in the paint 1a and 1b

Rating 1-5 (5 is excellent, 1 is poor)	Salt Spray, 500 hrs, Gardobond OC	Salt Spray, 500 hrs, Gardobond OC, 4 months ageing
ER3520/EK8545, no silane	1	2
ER3520/EK8545, MP200 in let down	5	1
ER3520/EK8545, MP200 emulsion in let down	5	1
ER6520/EK6870, MP200 emulsion in let down	4	1

Example 2

[0033] Example 2a, the process to prepare the co-dispersion of epoxy and silane in water is given in the first section of the examples. The silane emulsion can be fresh or even aged (at room temperature) for some weeks. Epoxy-silane blend of these examples are cold blend of EPI-REZ 6530-WH-53 with the MP200 emulsion. The MP200 emulsion can also be added during the process after the dilution step of the EPI-REZ 6530-WH-53 preparation. The temperature at this stage is around 58°C.

[0034] Example 2b is based on a 3 months old MP200 emulsion, mixed with EPI-REZ 6530-WH-53, then aged (at room temperature) for 1 year as a blend.

Table 3: composition of example 2a and 2b

Ingredients Part A	Weight, g
EPIKURE 8545-W-52	114.15
Dowanol PPH (Dow)	26.88
EFKA2526 (EFKA)	2.6
Ti-Pure R960 (DuPont)	86.74
Tremin 283-600AST (Sibelco)	85.17
Albawhite 80 (Sachtleben)	58.08
Heucophos CAPP (Heubach)	80.78
MicaS (Aspanger)	6.22
Additol VXW 6208 (Cytec)	5.63
Demi-water	87.89
Raybo 80 (Raybo Chemicals)	0.86

Ingredients Part B
EPI-REZ 6530-WH-53 with the MP200 emulsion	445.17
Total	1000

Rating 1-5 (5 is excellent, 1 is poor)	Salt Spray, 500 hrs, Gardobond OC
2a, with old epoxy-silane blend	4-5
2b, with fresh epoxy-silane blend	4-5

REFERENCES CITED IN THE DESCRIPTION

[0035] 

This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

[0036] 

US 6,221,934 page 1, line 12

WO 2011/112452 page 1, line 18

EP 1896522 page 2, line 11

Claims

1. A process to make a storage stable aqueous co-dispersion of an epoxy resin and at least a silane.

2. The process of claim 1 characterized in that the silane as emulsion is blended with a water-based epoxy resin or that the silane is added at the end of the preparation of the epoxy water based resin and preferably in presence of mono-functional epoxy reactive diluents.

3. The process of claims 1 or 2 characterized in that pigments and additives are added to the composition after the blend of the epoxy resin emulsion or dispersion and the silane.

4. The composition of the formulation according to claims 1 and 3 characterized in that the mono-functional epoxy reactive diluent has a linear or branched alkyl chain.

5. The composition of the formulation according to claims 1-5 characterized the composition is combined with water compatible curing agent containing optionally pigment, filler and additives.

6. The paint formulation based on the composition of claim 5 characterized in that the aqueous epoxy-silane of claims 1-4 is aged for 12 months at room temperature and provide excellent corrosion protection.